Electrochemical cells have been used for many years to produce or consume an electrical current by means of a chemical reaction. In the design and improvement of electrolyte and electrodes used in an electrochemical cell it is often necessary to determine where losses occur so that an attempt can be made to improve the voltage efficiency of the cell. As is well known, there are three principal types of voltage losses in an electrochemical cell; ohmic or IR polarization, activation polarization and concentration polarization. The IR polarization is associated with the voltage gradient that is necessary, to drive the charged ions through the cell electrolyte, and to drive electrons through the electrode and other conductive material. The activation polarization loss is somewhat harder to appreciate and is related to the irreversibility of the electrochemical reactions in the cell under current drain. The concentration polarization loss is the third source of voltage loss and is related to the resistance to mass transport of the reacting species. A more complete discussion of these losses is found in HANDBOOK OF FUEL CELL TECHNOLOGY by Carl Berger, published in 1968.
In the measurement of these voltage losses it is desirable to measure the activation polarization and concentration polarization independent of the IR polarization. One known way of making this IR correction to cell voltage utilizes the known fact that of the three different types of losses, the IR polarization loss is the only one which, in essence, changes almost instantaneously if the current through an electrochemical cell is varied. Accordingly, this method involves the use of an oscilloscope, or the like, which is connected to read the voltage level of the electrochemical cell. The current through the cell is interrupted; then, the resultant voltage change that occurs shortly after the current change, this time frame being on order of microseconds, is measured. Because the variables associated with the activation polarization losses and the concentration polarization losses have not yet been reflected in the voltage change, this initial voltage change reflects primarily only IR polarization losses.
There are a number of problems with this just mentioned method of measuring the IR polarization in an electrochemical cell. It is time consuming and has inherent inaccuracies associated with measuring the voltage changes within the precise time frame required; manual adjustment of the instrument is required if the cell is to be operated at a particular IR corrected potential; and these adjustments are not available to compensate the cell for rapid changes in IR.